1. Field of the Invention
This invention relates to a method of and an apparatus for controlling ignition timing in an internal combustion engine, more specifically to a method of and an apparatus for controlling ignition timing in an internal combustion engine wherein in a case where, after retarding the ignition timing for preventing knocking, the engine speed falls below a prescribed level or the engine otherwise moves into a region of operation where knocking control is unnecessary with the ignition timing still retarded, advancement of the ignition timing for eliminating the retardation is carried out gradually.
2. Description of the Prior Art
In a method of and an apparatus for controlling ignition timing in an internal combustion engine, it is a common practice to detect when knocking begins and then adjust the basic ignition timing to cause the knocking to stop. In this case, after the occurrence of knocking has been detected, the basic ignition timing is subjected to retarding adjustment until the knocking stops, whereafter it is subjected to advancing adjustment to bring it back to the basic ignition timing. After retarding adjustment of the ignition timing has been implemented for the purpose of eliminating knocking, it may happen that with the retarding adjustment still in effect the engine moves into an operating region in which knocking control is unnecessary, as when the engine speed falls below a prescribed level or some other predetermined operating condition or conditions occur. In such cases, it is generally necessary to restore the ignition timing to the basic ignition timing. One example of such a device is disclosed in Japanese Laid-open Patent Application No. 60-85252. In prior art however, this is accomplished by advancing the ignition timing to the basic ignition timing in a single operation and, as result, hunting is caused such as by the accompanying variation in torque and the drivability of the vehicle powered by the engine is degraded.